PubChem is a database of chemical molecules and their activities against biological assays, maintained by the National Center for Biotechnology Information (NCBI) of NIH.
PubChem consists of Compounds (pure and characterized chemical compounds), Substances (mixtures, extracts, complexes and uncharacterized substances) and BioAssay (bioactivity results from high-throughput screening). It serves as a free public database for drug/probe discovery.
ChemBank is a public, web-based database by the Broad Institute of freely available data derived from small molecules and small-molecule screens.
KEGG LIGAND Database
KEGG LIGAND Database is a publicly accessible database for chemical substances and reactions that are relevant to life.